Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 031924 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 325 PM EDT THU SEP 3 2015 .SYNOPSIS...A WEAK DISTURBANCE WILL PASS OVER NORTHERN NORTH CAROLINA TONIGHT. A BACKDOOR COLD FRONT WILL APPROACH FROM THE NORTH LATE FRIDAY... THEN PUSH SOUTHWARD THROUGH THE AREA FRIDAY NIGHT... BEFORE SETTLING TO OUR SOUTH ON SATURDAY. HIGH PRESSURE WILL NOSE IN FROM THE NORTH OVER THE WEEKEND. && .NEAR TERM /THROUGH TONIGHT/... AS OF 235 PM THURSDAY... CONVECTION CHANCES STILL LOOK PRETTY SLIM FOR THE REST OF THE DAYLIGHT HOURS IN CENTRAL NC. THE LATEST MESOANALYSES INDICATE PW VALUES NEAR OR BELOW NORMAL OVER THE NRN TWO THIRDS OF THE CWA... WITH SMALL MLCAPE OF 500 J/KG OR LOWER WITH CINH PERSISTING IN THE NORTHEAST CWA... AND VERY WEAK DEEP LAYER SHEAR. THE ONLY CONVECTION THUS FAR OUTSIDE OF THE VA MOUNTAINS HAS BEEN ACROSS EXTREME SE NC ALONG THE OLD OUTFLOW BOUNDARY AND BENEATH THE WEAK MID LEVEL SHEAR AXIS. BASED ON THE BOUNDARY LOCATION AND ATTENDANT LOW LEVEL MASS CONVERGENCE AS WELL AS MOISTURE AVAILABILITY... CONTINUE TO THINK THAT THE FAR SRN AND SE FRINGE OF THE CWA MAY STILL SEE ISOLATED SHOWERS AND STORMS OVER THE NEXT SEVERAL HOURS... GIVEN THAT LOW AND MID LEVEL LAPSE RATES ARE BEST ACROSS THIS SRN TIER. LOWER PW AND LOWER POTENTIAL FOR INSTABILITY ELSEWHERE WITH A LACK OF TRIGGER SHOULD PRECLUDE SHOWER/STORM DEVELOPMENT OVER THE REST OF THE CWA THROUGH EARLY EVENING. THEN AFTER NIGHTFALL... IT`S A TOUGH CALL ON WHETHER OR NOT WE`LL SEE ISOLATED SHOWERS OVERNIGHT. SOME SREF MEMBERS AS WELL AS THE NAM AND GFS SPIT OUT A LITTLE LIGHT PRECIP MAINLY N AND NE OF RDU... LIKELY A RESULT OF WEAK DPVA DRIFTING SOUTHWARD FROM VA AND/OR WEAK UPPER DIVERGENCE ALONG A SUBTLE UPPER SHEAR AXIS THAT WILL EXTEND FROM WV ACROSS NE NC LATE TONIGHT. IN EITHER CASE... COVERAGE AND AMOUNTS DO NOT APPEAR TO BE VERY HIGH... GIVEN THE WEAKNESS OF ANY POSSIBLE FORCING FEATURES AND THE ABSENCE OF ANY PRECIP LATE TONIGHT ON OTHER MODELS SUCH AS THE NSSL WRF. HOWEVER... WILL LEAVE IN A SLIGHT CHANCE OF SHOWERS ACROSS THE FAR N AND NE GIVEN THE GOOD AGREEMENT ON THE UPPER DIVERGENCE BAND. LOWS 67-72. -GIH && .SHORT TERM /FRIDAY AND FRIDAY NIGHT/... AS OF 325 PM THURSDAY... OUR BEST SHOT AT SCATTERED TO NUMEROUS SHOWERS AND STORMS WILL BE LATE FRI INTO FRI NIGHT... WITH SEVERAL FAVORABLE FACTORS IN PLAY. FIRST... MODELS DEPICT A POCKET OF ABOVE-NORMAL PW SLIDING SOUTHWARD FROM VA INTO/THROUGH CENTRAL NC TOMORROW... IN CONJUNCTION WITH WEAK DPVA SPREADING IN FROM THE NW AND NE AND IMPROVING UPPER DIVERGENCE FROM THE NORTH... ALL AHEAD OF THE INCOMING BACKDOOR COLD FRONT. THE LARGE-SCALE MODELS INCLUDING THE NAM/GFS/ECMWF/SREF ARE IN AGREEMENT ON CONVECTION DEVELOPING DURING THE EARLY TO MID AFTERNOON OVER CENTRAL NC... FOCUSING THE BEST COVERAGE AND HIGHEST AMOUNTS OVER THE FAR NW PIEDMONT. GIVEN THE EXPECTED MID-UPPER LEVEL DYNAMIC CONTRIBUTIONS TO ASCENT... DESTABILIZATION WITH GOOD HEATING DURING THE DAY... AND RISING MOISTURE THROUGH THE COLUMN... CONVECTIVE COVERAGE LOOKS SUFFICIENT TO RAISE POPS A BIT... TO LIKELY IN THE NW CWA WITH GOOD CHANCES ELSEWHERE FOR NOW (ALTHOUGH THESE MAY GO UP TO LIKELY HERE AS WELL IN LATER FORECASTS IF TRENDS HOLD). THE WEAK DEEP LAYER SHEAR SHOULD LIMIT STORM STRENGTH... ALTHOUGH THE PROFILE AND DCAPE NOTED ON NAM FORECAST SOUNDINGS WOULD SUGGEST A MARGINAL WIND THREAT. THE ANTICIPATED SLOW MOVEMENT WITH HIGH WATER CONTENT WILL BRING A RISK OF SLOW-MOVING STORMS GENERATING URBAN FLOODING. EXPECT HIGHS OF 90-95 WITH DECENT PREFRONTAL HEATING AND CONTINUED ABOVE NORMAL THICKNESSES. POPS SHOULD TREND DOWNWARD AFTER NIGHTFALL WITH LOSS OF INSOLATION... HOWEVER WITH LOW LEVEL CONFLUENT FLOW NEAR THE BACKDOOR FRONT AND INCREASED ATLANTIC-SOURCE FEED WITH PERSISTENT UPPER DIVERGENCE OVERNIGHT... WILL KEEP A MENTION OF SCATTERED SHOWERS AND STORMS THROUGH THE NIGHT... WITH THE BEST CHANCES WEST. LOWS 67-71. -GIH && .LONG TERM /SATURDAY THROUGH THURSDAY/... AS OF 150 PM THURSDAY... COOLER TEMPERATURES EXPECTED FOR MUCH OF THE LONG TERM AS THE COLD FRONT THAT IS PROGGED TO COME THROUGH FRIDAY NIGHT WILL BRING A CHANGE IN AIRMASS FROM THE NORTHEAST. WITH THIS WILL COME A GREATER FETCH OF MOISTURE FROM OFFSHORE...DRIVEN BY SEVERAL SHORTWAVE IMPULSES THAT ARE EXPECTED TO MOVE INTO THE STATE DURING THE WEEKEND AND INTO EARLY NEXT WEEK. FOR THE WEEKEND...THE GREATEST THREAT FOR RAIN WILL BE IN THE WEST ON SATURDAY AS THE FRONT MOVES THROUGH AND A CAD-LIKE SCENARIO SETS UP. AS THE WEEKEND PROGRESSES HOWEVER...AN INVERTED TROUGH ALONG THE EAST COAST WILL SHARPEN AND THUS BRING A MORE NORTHERLY COMPONENT TO THE WIND AND SHUT OFFSHORE MOISTURE FEED INTO THE NW PIEDMONT AND INSTEAD BEGIN TO FOCUS THE BEST CHANCE FOR CONVECTION OVER THE EASTERN PART OF THE STATE. THUS RAIN CHANCES FOR SUNDAY WILL BE BETTER IN THE EAST THAN IN THE WEST. THIS PATTERN WILL CONTINUE INTO LABOR DAY WITH SOUTHEASTERN COUNTIES HAVING THE BEST CHANCE FOR SHOWERS AND THUNDERSTORMS. HIGHS IN THE LOW TO MID 80S FOR THIS PERIOD WITH THE POTENTIAL FOR SOME UPPER 70S IN THE NW IF CLOUD COVER LOCKS IN. THE BERMUDA HIGH BEGINS TO TAKE BACK OVER FOR MIDWEEK AND THE SURFACE HIGH OVER OUR AREA AND THE INVERTED TROUGH WILL BEGIN TO BREAK DOWN. THIS WILL SEE A RETURN TO WARMER TEMPERATURES...ALTHOUGH GRADUALLY...WITH DIURNAL CHANCES FOR SHOWERS AND ISOLATED THUNDERSTORMS THROUGH THURSDAY. AT THIS TIME...ANY THUNDERSTORMS THAT DO OCCUR EITHER THIS WEEKEND OR NEXT WEEK ARE NOT EXPECTED TO BE SEVERE...BUT A FEW STRONG STORMS CANNOT BE RULED OUT. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/... AS OF 105 PM THURSDAY... VFR CONDITIONS WILL HOLD TODAY INTO THIS EVENING. A WEAK LOW PRESSURE TROUGH WILL REMAIN STRETCHED ACROSS SE NC AS WEAK HIGH PRESSURE HOLDS OVER NRN AND WRN NC. THERE IS A SMALL CHANCE OF A SHOWER OR STORM GENERATING BRIEF SUB-VFR CONDITIONS AT FAY TODAY MAINLY 19Z-01Z... BUT CHANCES ARE TOO LOW TO MENTION AT THIS TIME. THERE IS A RISK OF MVFR-IFR FOG LATE TONIGHT INTO EARLY FRI MORNING AT RDU/FAY AND ESPECIALLY RWI... WITH WINDS GOING CALM AND LITTLE IN THE WAY OF CLOUD COVER WITH RESIDUAL GROUND MOISTURE ALL FACILITATING FOG DEVELOPMENT ESPECIALLY IN LOW LYING AREAS. ISOLATED SHOWERS ARE POSSIBLE TONIGHT NEAR RDU/RWI... HOWEVER MODELS ARE NOT IN GOOD AGREEMENT ON THIS... AND ANY COVERAGE SHOULD BE LOW ANYWAY... SO WILL NOT MENTION IN THE TERMINAL FORECASTS FOR NOW. VFR CONDITIONS WILL AGAIN DOMINATE MID-LATE MORNING FRI... HOWEVER WE`LL SEE A TREND TOWARD NUMEROUS SHOWERS AND STORMS AREAWIDE TOWARD THE END OF THIS 24-HR FORECAST PERIOD... LIKELY STARTING NEAR OR JUST AFTER 16Z... AS A BACKDOOR COLD FRONT APPROACHES FROM THE NORTH. OUTSIDE OF ANY SHOWERS/STORMS... SURFACE WINDS WILL REMAIN LIGHT. LOOKING BEYOND 18Z FRI... CONFIDENCE IS HIGH THAT NUMEROUS SHOWERS AND STORMS WITH SLOW MOVEMENT WILL BRING A PERIOD OF ADVERSE AVIATION CONDITIONS TO ALL CENTRAL NC TERMINALS FRI AFTERNOON THROUGH MID EVENING. SUB-VFR CIGS/VSBYS... HEAVY DOWNPOURS... AND ENHANCED SURFACE WIND GUSTS WILL BE POSSIBLE IN/NEAR THIS ACTIVITY. THE COLD FRONT WILL PUSH SOUTHWARD THROUGH CENTRAL NC FRI NIGHT AND SETTLE TO OUR SOUTH SAT... HOLDING THERE WHILE WEAKENING THROUGH TUE AS HIGH PRESSURE NOSES IN FROM THE NORTH AND NE. SUB-VFR LOW CLOUDS AND FOG ARE LIKELY AT ALL SITES EACH LATE NIGHT/EARLY MORNING SAT/SUN/MON. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...HARTFIELD NEAR TERM...HARTFIELD SHORT TERM...HARTFIELD LONG TERM...ELLIS AVIATION...HARTFIELD

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